Description (adapted from the application): Enveloped viruses, such as retroviruses and vaccinia viruses, normally surround themselves with eukaryotic plasma membranes as part of their maturation within host cells. In the process of budding, these viruses not only incorporate their own envelope glycoproteins, but multiple host cell transmembrane proteins as well. This project is intended to test the hypothesis that during the normal maturation process, functional copies of CFTR protein can also be incorporated into envelopes of budding virions. We will co-express CFTR with vaccinia virus, or with the gag genes of Mason-Pfizer Monkey virus (M-PMV) or Rous sarcoma virus (RSV). The resulting pseudovirions will be used to target functional CFTR protein to epithelial cells that lack CFTR. In this way, we will determine whether viral capsids can be used to deliver functional CFTR in a pre-folded and active form to the membranes of CF epithelial cells in vitro and in vivo. These experiments are designed to use gene therapy vectors and technologies (virus pseudotyping, virus-based gene transfer, recombinant CFTR expression) to examine a simplified delivery system comprised of an empty viral capsid surrounded by a fusigenic envelope enriched in functional CFTR protein. If complex polytopic transmembrane proteins such as CFTR can be delivered to the cell surface in a folded and active form by pseudovirions, therapies for other genetic defects in membrane protein biochemistry might be studied in the same way.